1. Field of the Invention
The present invention relates to a brake system, particularly, relates to a caliper for use in a hydrostatic disk brake system and a wheel cylinder for use in a hydro static drum brake system, which are used in motor vehicles, airplanes, trains, etc. The present invention also relate s to a method for assembling the caliper of a hydrostatic brake system.
2. Related Art Statement
Hydrostatic brake system s are generally used for the braking systems of motor vehicles, airplanes, or trains. The hydrostatic brake system is roughly classified into a disk brake system and a drum brake system. In either systems, a braking operation is carried out in such a manner that a brake master cylinder works to pressurize brake fluid contained in the master cylinder responding to the braking operation by an operator, the pressure is transmitted to a caliper (disk brake system) or a wheel cylinder (drum brake system), and in the caliper or the wheel cylinder, a piston works to effect the braking operation in accordance with the pressure of the brake fluid.
During the braking operation, it is required that the piston is closely adhered onto the inside wall of the cylinder in the caliper body in order to prevent a leakage of brake fluid and to realize a smooth movement of the piston. Thus, in case of a disk brake system, a piston seal is provided inside of a caliper, while, in case of a drum brake system, a piston cup is provided inside of a wheel cylinder. In a disk brake system, a groove is provided inside of the cylinder of the caliper body to hold the piston seal therein. While, there are two types of drum brake system, one of which is a unified type where a groove is provided on an outer surface of the piston for holding the piston cup therein; the other one of which is a separated type where no groove is provided but the piston cup is brought into contact with the outer surface of the piston. The piston seal or the piston cup operates a pad or a lining via the piston to generate a braking force when the pressure of the brake fluid is transmitted.
In assembling such a caliper or a wheel cylinder, a piston seal or a piston cup being treated with an oil material on the surface thereof is used in order to make the assembling procedure easier. The operator sometimes uses grease to assemble the caliper or the wheel cylinder. However, the amount of grease used is very little and only for the purpose of making the assembling procedure of the piston seal or the piston cup into the caliper body or the cylinder body easy.
However, the caliper or the wheel cylinder assembled in the conventional manner has a problem as mentioned below.
In the conventional caliper for use in a disk brake system, when a brake pedal is stepped on to generate hydrostatic pressure, the piston of the brake system is pushed as well as the piston seal, then the piston seal is twisted. While, when the hydrostatic pressure is released, the twisted condition of the piston seal is retrieved so that the piston is aligned into its initial position by the self-aligning force of the piston seal. In such a caliper, if the caliper is used for a long time, the contact portion between the piston and the piston seal becomes not to work normally due to a variation of temperature of the outside, a variation of temperature when vehicles are running, rust, or dust generated by the piston seal, so that the piston becomes not to be returned properly. If the contacted portion between the piston and the piston seal does not work normally, so-called shaking phenomenon of the piston per se generates and such a movement of the piston may scratch the inner surface of the cylinder. By such an abnormal movement of the piston, so-called xe2x80x9cbrake dragxe2x80x9d or a leakage of oil would be caused so that the braking ability of the system would be decreased. Further, the disk pad would be abraded so much by this xe2x80x9cbrake dragxe2x80x9d phenomenon, a great amount of dust is generated from the pads during the braking operation and the dust is sprinkled in an atmosphere. The dust gives a non-healthy influence to human bodies and once the dust adheres onto wheels, etc., it is very difficult to remove it.
The conventional wheel cylinder has the same problem. In the conventional wheel cylinder, since only a small amount of grease is used for assembling the piston cup into the wheel cylinder, if such a wheel cylinder is used for a long time, the piston operation would not work well by a friction caused between the piston cup and the cylinder body.
The present invention is carried out in order to solve the above-mentioned problem. The first aspect of the present invention is a caliper for use in a disk brake system, which comprises at least a caliper body having a cylinder portion, a piston, a piston seal and dust boots, said caliper body having a first groove for holding said piston seal and a second groove for holding said dust boots, and said piston having a third groove for holding said dust boots; wherein at least a space formed between the first groove for positioning said piston seal, which is provided in an inside surface of the cylinder portion of said caliper body, and said piston seal being positioned in said first groove, a space between an outer side surface of said dust boots and said caliper body, in a space between an inner side surface of said dust boots and said piston, and a space formed by said dust boots, said caliper body, said piston and said piston seal, are filled with grease.
According to the first aspect of the present invention, out of the portions where the piston seal and the piston are made to contact together in the caliper of the disk brake system, the inside from the piston seal would be covered by an oil film of a brake fluid, while, the outside from the piston (the dust boots side) is covered by an oil film of the grease. Therefore, it can be prevented that the temperature at this contact portion becomes high or that the operation of the caliper becomes out of order due to an impurity such as rust or dust, so that it becomes possible to keep the movement of the piston seal and the piston in the best condition for a long time. In this manner, in the caliper according to the present invention, the piston always works in a proper condition and therefore only the pressure of brake fluid transmitted from the master cylinder is properly applied to the contact portion of the piston and the piston seal so that the force of the piston is transmitted to the disk pad without generating any excessive force.
In the caliper of the disk brake system according to the present invention, it is preferred to provide another groove on the inside surface of the cylinder of the caliper body between the first groove formed in said caliper body for positioning said piston seal and the second groove for positioning said dust boots. Because, the grease is apt to be kept in the third groove, so that it becomes easy to hold the grease in the really necessary portion, i.e. the space formed by the dust boots, the caliper body, the piston and the piston seal.
The present invention can be applied not only to a normal type (opposite piston type) of caliper but also to a floating type of caliper. In the floating type caliper, the caliper body is movably installed with the aid of a pin, and a connecting portion for connecting the caliper body and said pin is covered by dust boots. According to the invention, it is required that a sufficient amount of grease exists in a space formed by the dust boots and the pin, in a space formed between the dust boots and an inner surface of a pin receiving section of the caliper body, and in a space formed between an outer surface of the pin and the inner surface of the pin receiving section of the caliper body.
The second aspect of the present invention is a wheel cylinder for use in a drum brake system which comprises at least a cylinder body, a piston which is to be positioned inside of said cylinder body, a cup seal provided between said cylinder body and said piston, dust boots for covering said cylinder body and said piston, wherein at least a space formed between said piston and said cup seal and a space formed by said piston, said cylinder body and said dust boots are filled with grease.
In this manner, in the drum brake system, it also becomes possible to prevent an abnormal operation of the wheel cylinder by filling the space between the piston and the cup seal, and the space formed by the piston, the cylinder body and the dust boots with grease, and thus the piston works in a stable manner for a long time.
Further, when assembling the caliper for use in a disk brake system, it is preferred that when installing the piston into the caliper body, said grease is applied at least a half of the outer surface of the piston from its inserting side, then penetrating the piston having the grease on the half of the outer surface thereof into the caliper body (cylinder portion), so that the grease exists in the space formed by the dust boots, the caliper body, the piston and the piston seal sufficiently.
According to this assembling method, it becomes possible to put a sufficient amount of grease in a desired portion, i.e. the space formed by the piston, the piston seal, the dust boots, very easily.
Furthermore, when assembling the caliper for use in a disk brake system, it is preferred that when installing the piston into the cylinder portion, after penetrating said piston into the cylinder from the top portion of the piston until the top portion reaches to the sequel of the piston seal, then extracting the piston once, and then applying the grease and penetrating the piston into the caliper body again. By this operation, the initial fitting of the piston and the piston seal becomes better.
It should be noted that if the operation of penetrating and extracting the piston is repeated, applying some grease on the surface of the piston, the fitting of the piston and the piston seal becomes much better and a sufficient and proper amount of grease can exist in the desired space easily.